Investigation of Crystallization Behavior and Mechanical Properties of Polyetherether-Ketone with Celluloase Nanocrystals and Graphene Nanoplate Composites

Abstract

In this study, the crystallinity and mechanical properties of PolyEtherEther-Ketone (PEEK)-based nanocomposites with additive nanoparticles like graphene nanoplate (GNP) and cellulose nanocrystals (CNC) in the compression molding process have been investigated. First, the powder was packed in a temperature room with high pressure (350 bar). Then, composites were fabricated at 400˚C at 20 bar pressure and cooled down to room temperature at different cooling rates from 0.7˚C/min to 400˚C/min. Crystallization of neat PEEK, as a reference, has been compared to PEEK CNC and PEEK CNC/GNP to investigate the influence of graphene nanoplate and cellulose nanocrystals on the crystallization of PEEK. The crystallization kinetic of PEEK was studied by differential scanning calorimetry (DSC). Mechanical behaviors of composites were examined using tensile and impact tests. DSC results revealed that CNC/GNP-filled PEEK crystallization has better crystallinity than neat PEEK because the nanoparticles promote high-density nucleation sites and accelerate the heterogeneous nucleation rate. Also, nanoparticles decrease the cold crystallization temperature of PEEK and restrict the mobility of PEEK chains caused, reducing the strain of failure. In all Samples, the crystallinity decreased in the higher cooling rates. Regarding mechanical properties, the neat PEEK had a higher absorbed energy impact than CNC/GNP or CNC PEEK composites. Also, the higher cooling rate decreases the PEEK crystallinity and reduces the tensile strength and Young modulus of the PEEK nanocomposites. It is found that the cooling rate has a significant effect on the PEEK crystallinity, as if no addition of nanoparticles could compensate for the low ratio of crystallinity at a high cooling rate. Due to the low cooling rate and high-pressure during compression molding, this process can increase the PEEK nanocomposite crystallinity more than other processes like injection molding. Therefore, the strength and stiffness of samples fabricated in compression molding are higher than those in injection molding.